The present invention relates to irrigation systems, and more particularly, to rain sensors which interrupt the execution of a watering program by an electronic irrigation controller during periods of rainfall.
In many areas of the world, it is necessary to irrigate crops and landscaping due to inadequate seasonal rainfall. Within the past several decades electronically controlled irrigation systems have come into widespread use. They typically include a micro-processor based irrigation controller which executes a stored watering program for turning on and off valves connected to supply lines equipped with sprinklers. The watering program typically activates various zones during run cycles measured in minutes on selected days of the week. The watering program can be adjusted to accommodate seasonal variations in rainfall. However, due to the unpredictability of weather patterns in general, it is desirable to connect a rain or moisture sensor to an electronic irrigation controller so that the sprinklers will not be turned on while it is raining, and for some time period thereafter before the rainfall has either evaporated or soaked into the ground. By interrupting a watering program of an electronic irrigation controller during, and shortly after, a period of rainfall, both purified and reclaimed water can be conserved thus lessening the demand on purification plants, reservoirs and other artificial delivery systems.
Rain sensors and moisture responsive actuators have been developed for use in connection with electronic irrigation controllers. One type of rain sensor operates in response to the weight of rainfall collected in a receptacle. However, this type of rain sensor is adversely affected by wind conditions and the collection of debris, and is too slow in reactivating the watering program. Its evaporative rate is not adjustable. Subterranean moisture sensors have also been developed for use with irrigation controllers. However, they are expensive, unreliable and subject to breakdowns. Rainfall sensors have also been developed which utilize infrared emitter and detector devices that optically detect the presence of collected rainfall. See for example U.S. Pat. No. 5,836,339 of Klever et al. entitled RAINDROP COUNTER AND CONTROL SYSTEM FOR IRRIGATION CONTROL SYSTEMS. However, these devices are relatively complex and expensive. Another category of rain sensor which has been widely commercialized under the MINI-CLIK® trademark utilizes a plurality of stacked discs made of a hygroscopic material. The discs expand in response to contact with rain water to depress a spring biased switch to deactivate the watering program of the electronic irrigation controller. When the rain stops, the hygroscopic discs eventually dry out and contract, thereby releasing the switch to re-activate the watering program. See for example U.S. Pat. No. 3,808,385 of Klinefelter entitled MOISTURE RESPONSIVE SWITCH ACTUATOR.
A principal drawback of rain sensors that utilize hygroscopic material lies in the fact that they require that an electrical switch be connected mechanically to the hygroscopic material. This allows the physical expansion of the hygroscopic material during rain fall, and subsequent contraction of the hygroscopic material during sunny conditions, to actuate the electrical switch between OFF and ON states to thereby generate the watering program interrupt and resume signals. The required mechanical connection between the electrical switch and the hygroscopic material necessarily entails some sort of elastomeric seal, boot or other waterproof flexible interface between an actuating element, such as a lever or pushbutton and a watertight case enclosing the movable conductive contacts of the electrical switch. Over time this elastomeric interface degrades, eventually allowing moisture to enter the watertight case. This leads to corrosion and other failures associated with the movable conductive contacts of the electrical switch. As a result, the irrigation controller may end up commanding the stations of the irrigation system to water during rainfall and/or fail to resume watering after it has been several days since rainfall and watering is required to prevent turf from browning and plants from dying. Thus there is a need for an improved rain sensor that will overcome the shortcomings of the interrupt system disclosed in U.S. Pat. No. 6,452,499 granted to Runge et al. on Sep. 17, 2002 entitled WIRELESS ENVIRONMENTAL SENSOR SYSTEM. The system of Runge et al. employs a rain sensor requiring an electrical switch connected mechanically to the hygroscopic material.